Soho Cds–nis in-flight intensity calibration using a plasma diagnostic method

The internal intensity calibration of the Coronal Diagnostic Spectrometer (CDS) – Normal Incidence Spectrometer (NIS) is studied using the Arcetri diagnostic method. A large number of spectral lines observed by the CDS–NIS 1 and NIS 2 windows in a solar active region is analysed in order to determine the intensity calibration curve for both channels. The plasma diagnostic method developed in Arcetri allows the measurement of the correction factors to the preliminary CDS–NIS internal intensity calibration curves and the determination of the relative calibration between NIS 1 and NIS 2. A further correction factor of approximately three is found to be necessary for a correct intercalibration of the two wavelength windows. Also the NIS 2 second-order sensitivity is measured. The Arcetri diagnostic method proves to be a powerful tool for intensity calibration studies.     

First XMM-Newton observations of strongly magnetic cataclysmic variables – II. Timing studies of DP Leo and WW Hor

XMM-Newton was used to observe two eclipsing, magnetic cataclysmic variables, DP Leo and WW Hor, continuously for three orbital cycles each. Both systems were in an intermediate state of accretion. For WW Hor we also obtained optical light curves with the XMM-Newton Optical Monitor and from ground-based observations. Our analysis of the X-ray and optical light curves allows us to constrain physical and geometrical parameters of the accretion regions and derive orbital parameters and eclipse ephemerides of the systems. For WW Hor we directly measure horizontal and vertical temperature variations in the accretion column. From comparisons with previous observations we find that changes in the accretion spot longitude are correlated with the accretion rate. For DP Leo the shape of the hard X-ray light curve is not as expected for optically thin emission, showing the importance of optical depth effects in the post-shock region. We find that the spin period of the white dwarf is slightly shorter than the orbital period and that the orbital period is decreasing faster than expected for energy loss by gravitational radiation alone.     

Tremolite decomposition on Venus II. Products, kinetics, and mechanism

We present revised tremolite powder thermal decomposition kinetics using previous and newly acquired data from longer time (years instead of months) and lower temperature experiments (<1073 K). We also present kinetic results for decomposition of millimeter- to centimeter-sized tremolite grains. Natural tremolite samples were heated at ambient pressure in flowing CO₂ or N₂ gas from 1023-1238 K. The tremolite decomposition products are a physical mixture of two pyroxene solid solutions (with the bulk composition Dp₅₉En₄₁), a silica polymorph, and water vapor. Decomposition rates were calculated by using the mass loss of the heated samples. Tremolite crystals and crystalline powder decompositions follow different but related Avrami-Erofe'ev (nucleation and growth) kinetic models. The rate equations for thermal decomposition of tremolite crystalline powder and the larger crystal grains are log₁₀k_powder (h⁻¹)=18.69(±0.19)−23,845(±833)/T and log₁₀k_crystal (h⁻¹)=19.82(±0.07)−25,670(±916)/T. The associated apparent activation energies are 456(±16) kJ mol⁻¹ and 491(±18) kJ mol⁻¹, respectively. We propose a decomposition mechanism and suggest that decomposition and dehydroxylation occur simultaneously. The rate-limiting step is proposed to be structural rearrangement of the amphibole structure to the two pyroxenes and silica. This step and the overall decomposition rate are predicted to be independent of pressure from 1 to 100 bars. These kinetic analyses strengthen our previous conclusion (Johnson and Fegley, 2000, Icarus 146, 301-306) that if hydrous minerals, such as tremolite, formed on Venus during a wetter past, then these minerals could still exist at current conditions on Venus' surface today.     

Mercury's sodium exosphere

Mercury's neutral sodium exosphere is simulated using a comprehensive 3D Monte Carlo model following sodium atoms ejected from Mercury's surface by thermal desorption, photon stimulated desorption, micro-meteoroid vaporization and solar wind sputtering. The evolution of the sodium surface density with respect to Mercury's rotation and its motion around the Sun is taken into account by considering enrichment processes due to surface trapping of neutrals and ions and depletion of the sodium available for ejection from the surfaces of grains. The change in the sodium exosphere is calculated during one Mercury year taking into account the variations in the solar radiation pressure, the photo-ionization frequency, the solar wind density, the photon and meteoroid flux intensities, and the surface temperature. Line-of-sight column densities at different phase angles, the supply rate of new sodium, average neutral and ion losses over a Mercury year, surface density distribution and the importance of the different processes of ejection are discussed in this paper. The sodium surface density distribution is found to become significantly nonuniform from day to night sides, from low to high latitudes and from morning to afternoon because of rapid depletion of sodium atoms in the surfaces of grains mainly driven by thermal depletion. The shape of the exosphere, as it would be seen from the Earth, changes drastically with respect to Mercury's heliocentric position. High latitude column density maxima are related to maxima in the sodium surface concentration at high latitudes in Mercury's surface and are not necessarily due to solar wind sputtering. The ratio between the sodium column density on the morning side of Mercury's exosphere and the sodium column density on the afternoon side is consistent with the conclusions of Sprague et al. (1997, Icarus 129, 506-527). The model, which has no fitting parameters, shows surprisingly good agreement with recent observations of Potter et al. (2002, Meteor. Planet. Sci. 8, 3357-3374) successfully explaining their velocity and column density profiles vs. heliocentric distance. Comparison with this data allows us to constrain the supply rate of new sodium atoms to the surface. We also discuss the possible origins of the strong high latitude emissions (Potter and Morgan, 1990, Science 248, 835-838; 1997a, Adv. Space Res. 19, 1571-1576; 1997b, Planet. Space Sci. 45, 95-100; Sprague et al., 1998, Icarus 135, 60-68) and the strong variations of the total content of the sodium exosphere on short (Potter et al., 1999, Planet. Space Sci. 47, 1441-1449) and long time scales (Sprague et al., 1997, Icarus 129, 506-527).     

Evaluation of Passive Diffusive-Adsorptive Samplers for Use in Assessing Time-Varying Indoor Air Impacts Resulting from Vapor Intrusion

Passive diffusive-adsorptive samplers are being considered for vapor intrusion (VI) pathway assessment, particularly where multi-week time-weighted average concentrations are desired. Recent studies have shown that passive samplers can produce accurate results under well-controlled steady concentration conditions, and field performance was also demonstrated at several sites. The objective of this study was to examine passive sampler performance in settings with time-varying indoor air concentrations, through a comparison of passive sampler results to concentrations determined by 24-h active sorbent tube sampling in a series of multi-week deployments. Sampling was performed in a well-instrumented residential building as well as industrial buildings, over periods of time ranging from 1 to 7 weeks. Strong linear correlations were noted between passive and active sampling concentration results for some passive samplers, with passive sampling results being similar to or lower than measured active sampling results by about 50% for those samplers in the residential study and about 25% higher in the industrial building study. Other samplers produced poor agreement. The conclusion from this study is that some passive samplers have great potential for use in multi-week indoor air quality monitoring. It was further determined that there is need for accepted procedures to validate and calibrate passive samplers for use in the field.     

Geochronology in the southern Midyan terrane: a review of constraints on the timing of magmatic pulses and tectonic evolution in a northwestern part of the Arabian Shield

The southern Midyan terrane is a composite Tonian to Ediacaran tectonostratigraphic crustal block in the northern Arabian Shield that prior to Red Sea opening was contiguous with coeval rocks in the Eastern Desert of Egypt and Sinai. Ion microprobe (sensitive high-resolution ion microprobe [SHRIMP]) dating of 12 rock samples described here and the results of other dating programmes establish a clear timeframe for depositional, intrusive, and structural events in the region and provide a chronology of tectonism in this part of the Arabian-Nubian Shield. Deposition of Zaam and Bayda group volcanosedimentary rocks and emplacement of mafic-ultramafic complexes and TTG-type diorite, tonalite, and granodiorite denote formation of the Tonian (780–715 Ma) Zaam arc and fore-arc ophiolite above a possible west-dipping subduction system in the southern part of the Midyan terrane. Convergence with the Hijaz terrane farther south and obduction of ophiolite nappes resulted by ~700 Ma in development of the Yanbu suture. Ongoing or a new subduction system led to a ~705–660 Ma Cryogenian pulse of magmatism represented by I-type calc-alkaline diorite, granodiorite, and granite that have volcanic-arc and syn-collisional granite affinities. This was followed, after a brief end-Cryogenian hiatus, by a 635–~570 Ma period of Ediacaran magmatism marked by monzogranite, syenogranite, and minor gabbro and diorite. These rocks are reported to have within-plate to volcanic-arc and syncollision chemical characteristics but their precise tectonic setting is uncertain. Structurally, the intrusions are diapiric and were evidently emplaced in an extensional regime consistent with an overlap between intrusion and Najd faulting associated, at this time, with transpressional collision and northward extension through much of the ANS. Terminal magmatism in the southern Midyan terrane postdated cessation of Najd faulting at ~575 Ma and resulted in the emplacement of undeformed within-plate A-type alkali-feldspar granites and mafic (lamprophyre) and felsic dikes.     

In-use energy and CO<Subscript>2</Subscript> emissions impact of a plug-in hybrid and battery electric vehicle based on real-world driving

Facilitated by fuel economy, climate legislation and government policy, sales of light-duty plug-in hybrid and battery electric vehicles are rapidly increasing during the last decade. But their energy and emissions impact have not been fully investigated, particularly accounting for energy and emissions during electricity generation. In this study, we conducted in-use energy consumption and emissions measurements of a plug-in and a battery electric vehicle under real-world city and highway driving conditions. We further compare them with energy consumption and emissions from counterpart conventional vehicles under the same driving conditions, to exclude benefits due to different vehicle specifications. Our results show that both the plug-in hybrid and battery electric vehicles can achieve about 50% energy benefits compared with their counterpart conventional vehicles, mainly through capturing regenerative energy. But when vehicles are tested in high-speed or high-acceleration driving conditions, the distance-normalized life-cycle CO₂ emissions of plug-in hybrid and battery electric vehicles are higher to their counterpart gasoline powered vehicles. The CO₂ emissions comparison results can vary based on the location and time of electricity generation. Therefore, our results confirm that benefits of promoting electric vehicles should consider temporal and spatial aspects of electricity generation.     

Tropicalization of the Northern Gulf of Mexico: Impacts of Salt Marsh Transition to Black Mangrove Dominance on Faunal Communities

The tropically associated black mangrove (Avicennia germinans) is expanding into salt marshes of the northern Gulf of Mexico (nGOM). This species has colonized temperate systems dominated by smooth cordgrass (Spartina alterniflora) in Texas, Louisiana, Florida and, most recently, Mississippi. To date, little is known about the habitat value of black mangroves for juvenile fish and invertebrates. Here we compare benthic epifauna, infauna, and nekton use of Spartina-dominated, Avicennia-dominated, and mixed Spartina and black mangrove habitats in two areas with varying densities and ages of black mangroves. Faunal samples and sediment cores were collected monthly from April to October in 2012 and 2013 from Horn Island, MS, and twice yearly in the Chandeleur Islands, LA. Multivariate analysis suggested benthic epifauna communities differed significantly between study location and among habitat types, with a significant interaction between the two fixed factors. Differences in mangrove and marsh community composition were greater at the Chandeleurs than at Horn Island, perhaps because of the distinct mangrove/marsh ecotone and the high density and age of mangroves there. Infaunal abundances were significantly higher at Horn Island, with tanaids acting as the main driver of differences between study locations. We predict that if black mangroves continue to increase in abundance in the northern GOM, estuarine faunal community composition could shift substantially because black mangroves typically colonize shorelines at higher elevations than smooth cordgrass, resulting in habitats of differing complexity and flooding duration.